I'm not sure how many more times we'll need to be told this before it sinks it, but time is certainly running out: According to the International Energy Agency , if we don't radically overhaul our energy supply, quickly moving away from fossil fuels and towards low-carbon sources, "the door will be closed forever " and dangerous climate change will be inevitable. And we have just five years before that door closes, the IEA says. The reason: The extent of existing fossil fuel-powered energy infrastructure and the rate with which new fossil fuel power plants are being built. If we are to hold carbon in the atmosphere to 450 parts per million—the level generally politically agreed upon in international climate negotiations but which is 100ppm higher than an increasing number of scientists say is safe—then we must radically increase the amount of low carbon energy being used. ...